In vehicle engines of current design, the carburetion or fuel injection system is provided with an idle air control system controlled by the vehicle engine control module (ECM). Typically, this comprises a fuel injection system of the throttle body injection type with an idle air inlet at the venturi adjacent the throttle valve. The volume of idle air inlet is controlled by an idle air valve which is actuated by a stepper motor. The engine idle speed is controlled by the ECM in response to various engine parameters by the controlled energization of the stepper motor. A driver circuit in the ECM produces first and second out-of-phase, sequence-controlled pulse trains for energizing the respective coils of the stepper motor for direction and displacement control thereof. The pulse trains, for example, have a constant frequency of sixteen pulses per second and the motor is rotated a fixed increment in response to each sequence step in the pulse trains with the direction of rotation being dependent upon the phase sequence of the pulse trains. The ECM controls the number of steps in order to obtain a desired setting of the idle air inlet valve.
Testers are already known for testing the stepper motor of an idle air control system in a vehicle engine without removing the motor. Such a tester comprises, in general, a driver pulse generator for generating the pair of pulse trains for respective stepper motor coils and a manually actuated switch for controlling the phase sequence and time duration of the pulse trains. The tester allows for testing of the motor for correct functioning and response to commands for correct idle speed.
In addition to testing the stepper motor for proper operation, it is desired to monitor the pulse trains from the driver circuits to ensure that they are uninterrupted throughout the duration of an ECM commanded idle air adjustment.
A general object of this invention is to provide an improved idle air control system tester with a monitor for stepper motor pulse trains and to overcome certain disadvantages of the prior art.